Which element has an isotope with 78 protons?

• A. Iridium
• B. Gold
• C. Mercury
• D. Platinum

Answer: (D)

Verified step by step guidance

1. Recall that the number of protons in an atom defines the element and is called the atomic number (Z).
2. Identify the atomic numbers of the given elements: Iridium (Z = 77), Gold (Z = 79), Mercury (Z = 80), and Platinum (Z = 78).
3. Since the problem asks for the element with an isotope that has 78 protons, look for the element whose atomic number is 78.
4. Recognize that the element with atomic number 78 is Platinum, meaning all isotopes of Platinum have 78 protons.
5. Conclude that the element with an isotope containing 78 protons is Platinum.